This invention relates generally to a fuel control system and method and more particularly to a fuel control system for a vehicle having a high power to weight ratio wherein an operator commanded power signal is compared to a sensed power signal for controlling the engine response to the difference therebetween.
While the invention will be described in conjunction with a diesel-type engine, it is to be understood that the basic principles of the invention may also be applied to a spark-ignited engine. In a conventional diesel engine with an electronic fuel control including an electronic governor, the controller typically operates as a speed controller and for many purposes this type of control is entirely satisfactory. However, in a passenger car with a relatively high power to weight ratio, high relative to for example trucks, the vehicle response, or driveability, suffers somewhat with a conventional speed control device since small changes in the operator's input result in large changes in torque output of the engine.
In conventional spark ignition engines, prior to the application of severe emission control constraints and very lean operation for better fuel economy, the engines were operated in the rich regime. In such modes of operation, the torque output of the engine is proportional to manifold pressure which results from air flowing into the cylinder past the throttle plate. The throttle plate acts as a restriction to the air flowing into the engine. When the pressure across any orifice, for example the throttle plate orifice, exceeds a certain ratio to the total inlet pressure, the velocity of the air particles through the orifice become sonic. This type of flow is referred to as sonic, critical or choked flow. In that condition, the quantity of air flowing through the orifice is independent of the pressure downstream of the orifice, and is only influenced by the upstream pressure and the orifice area.
When a conventional spark ignited engine operates at heavily throttled conditions (part load), the engine is operated with a nominally constant air/fuel ratio and the power output is directly related to air flow. Since this air flow is only related to throttle area during sonic flow conditions, the power output of the engine is therefore directly related to throttle area which, in turn, is directly related to throttle rotation caused by the operator.
Such performance characteristics, the direct relationship of throttle pedal movement to power output, is considered by most drivers to represent good driveability, or to have a good response characteristic of the operation of the engine in response to a throttle change. This invention describes a method and apparatus for achieving this good driveability type power control over a wide range of throttle inputs. The description will proceed as the invention is applied to a diesel engine fuel control to improve the throttle response characteristics of the engine and make the engine generally more satisfactory to the driver without sacrificing emissions or performance characteristics.
Accordingly, it is a primary object of the present invention to improve the driveability characteristics of internal combustion engines.
Other objects, features and advantages of the present invention will become readily apparent upon analyzing this specification and the associated drawings in which the single figure of the drawing is a schematic block diagram illustrating the principles of the present invention.